The present invention concerns tubes in composite material including carbon fibers embedded in a resin and, more particularly, such tubes of which at least one extremity is equipped with a sleeve allowing two coaxial tubes to be immobilized together. The invention also concerns support devices of the three-leg or one-leg type, for example used in the field of filming or measurement taking.
It is well known that the use of composite materials including carbon fibers embedded in an epoxy resin brings characteristics of a higher mechanical resistance for a relatively low weight.
Document FR-A-2 772 301 describes such an element in composite material and its fabrication process. A gel is disposed on a mandrel so as to create a superficial layer which provides good sliding characteristics on the internal wall of the finished tube, then it is prepolymerized. Subsequently, the layers of fabric with carbon fibers are applied and cooked at appropriate temperature until complete polymerization. An exterior layer of an additional gel can promote the constitution of an exterior surface with a low friction coefficient.
The tubes or cylinders in carbon can only be made with relatively short lengths, which makes it necessary, for many applications, to realize a connection between several successive tubes to obtain the required length for the application.
Document U.S. Pat. No. 4,941,692 thus provides profiled adhesive couplings between successive tubes, where a sleeve in appropriate resin also containing carbon fibers is placed in the junction zone to reinforce the longer tube thus obtained.
When the tubes must present lengths which are able to vary, it is preferable to use a telescopic assembly utilizing the gels of document FR-A-2 772 301 to ensure the relative sliding of the tubes. However, in that case, a means for fixing the total length is required. An extremity of the tube is then advantageously provided with a sleeve optionally equipped with a thread to allow cooperation with a tightening part or the like. In such case, the sleeve must be solidly anchored to the carbon tube, which is contrary to the low superficial friction coefficient of the carbon tubes.
The present invention is situated in this context and provides an assembly comprising a primary tube in composite material equipped with a sleeve which makes it possible to avoid the above-described drawbacks, the sleeve being provided to ensure a junction by tightening of a coaxial secondary tube.
According to the invention, the assembly comprises a primary tube in composite material including carbon fibers embedded in a resin, one extremity of which is equipped with a sleeve in plastic material, such as a polyamide, optionally equipped with a jointing thread, the sleeve being obtained by overmolding injection of material on the tube.
Preferably, the tube comprises at least two adjacent layers of carbon fibers, the inner layer being a layer whose fibers are substantially longitudinal, whereas the outer layer comprises helically arranged fibers.
Preferably, the material constituting the sleeve is reinforced with short fibers, so as to have a thermic dilatation coefficient approximately equivalent to that of the tube over a temperature range comprised between about xe2x88x9250xc2x0 C. and about +100xc2x0 C. These short fibers can advantageously be glass fibers.
Advantageously, the extremity of the tube equipped with the sleeve has a plurality of embossments which are filled with the sleeve material during the overmolding injection step.